Gold microdiscs as alkali preferential condensation spots for cell clock long-term frequency improvement

One of the main source of long-term frequency instabilities in MEMS cell clocks is the light-shift induced by optical intensity changes which can be caused by the presence of condensed alkali droplets within the light-path of the interrogation laser. We report here on the use of patent pending gold micro-discs as alkali preferential condensation spots in order to concentrate the alkali droplets outside of the laser light-path. Evidenced of preferential condensation of Rb on Au micro-discs is reported and the effect on the long-term frequency stability of a CPT clock setup are assessed.